In 2011, an estimated 230,480 new cases of invasive breast cancer were expected to be diagnosed in the U.S. and 39,520 women were expected to die from the disease. The standard care for these patients is surgery followed by radiotherapy, which has been shown to significantly decrease the risk of loco-regional tumor recurrence.
Modern radiotherapy is known for its extremely high geometrical accuracy targeting at the tumors. For most cancers treated by radiotherapy, an accuracy of 3 mm is achieved. However, the accuracy of breast treatment is an order of magnitude worse due to poor set up and immobilization techniques. Breast setup and immobilization have been a persistent problem. The challenge can be appreciated from FIGS. 1A and 4A showing breast tissue when a patient is set up in the supine position without any form of breast support. The breast tissue is naturally pulled towards the patient chest by gravity. In order to treat the breast using a whole breast irradiation technique, the radiation field has to cover the entire volume marked by the intersecting line, including part of the heart and the lung. The over inclusiveness of the radiated tissue could lead to severe long term side effects. For example, the skin fold, where the pendulous breast is in contact with the chest skin, will receive a full dose from the radiation treatment, resulting in painful skin erythema and long term side effects as shown in FIG. 2A. Due to the uncertainty in the breast shape and position, a large geometrical margin has to be used that leads to increased normal breast tissue dose in partial breast irradiation method. This additional margin requirement necessitates treatment of larger volumes of normal breast tissue and recent reports have suggested that external beam partial breast irradiation may be associated with increased toxicity, specifically subcutaneous fibrosis and suboptimal cosmetic outcome (FIG. 2B).
In FIGS. 1B and 4B, a breast is shown in the prone position without any form of breast support. Radiotherapy in the prone position can improve the radiation dosimetry. The advantages are obvious that, due to the greater distance between the breast and patient body and the disappearance of mammary skin fold, lower toxicities to normal organs other than the breast are achievable. On the other hand, the prone position cannot be tolerated by many patients for repeating daily treatment. Also, the setup time is longer and the setup uncertainties are greater than treatments in the supine position. Furthermore, lymph nodes cannot be easily treated in this prone position. Due to these reasons, most patients will still be treated in the supine position that is associated with poor treatment accuracy and higher risk of severe toxicity.
A number of devices have been proposed to assist breast set up in the supine position. These devices include the breast thermoplastic cast shown in FIG. 3A. For this thermoplastic cast, the thermoplastic material is firm at room temperature but becomes moldable when heated up to 60° C. It can be then used to create masks that conform to patient breast contour. Thermoplastic masks are widely used in the immobilization of head and neck patients where sufficient bony structures can be immobilized by the mask. Its application in breast immobilization, though, has been unsuccessful due to the lack of rigidity in the breast tissue. It also increases radiation skin dose and leads to more severe skin reactions. A vendor has recently removed the thermoplastic cast product from their catalog.
A second type of existing breast support device for use in the supine position is the breast ring shown in FIG. 3B. The breast ring device consists of a reinforced polyvinylchloride tube formed into a ring that is placed around the breast. A strap around the patient's chest holds the ring in place. The breast ring provides very limited improvement in the breast position, though, at a cost of significantly higher skin dose at areas in contact with the ring. The breast ring idea was first published in 1994, but has never found much clinical acceptance.
A third type of existing breast support device is a plastic cup with or without vacuum as shown in FIG. 3C and described in U.S. Pat. Nos. 8,210,899; 7,742,796 and 7,597,104. Plastic cups with vacuum (i.e., suction cups) were experimented with as breast immobilization devices and found some success when the patient is not in the supine position. Breast tissue with suction cup support is shown in FIG. 4C. Nonetheless, the shear force applied on the skin would be too high to tolerate when the cups are used to lift the breast against gravity. As a result of these failed attempts, there are currently no viable commercial suction cup products. Typically, patients are either treated these days without any breast set up and immobilization device, or with improvised methods such as bubble wraps, tapes or straps that result in very poor positioning accuracy.
Other prior art efforts at breast immobilization are described in U.S. Pat. Nos. 6,418,188; 7,828,744; 7,489,761 and 6,146,377.